fun or maybe stupid?

I was thinking of making a blade fury/light trap assassin using infinity runeword (yes on the assassin not the merc) so i need to know does the
-lightning res work for traps? and as for the loss of ignore target def i would use a might or holy freeze merc using pride
as for the other items a mix of blade fury equipment and some +skills for trap dmg

No, not stupid at all now that I think of it. Infinnity will make your traps hurt, and high damage + crushing blow and lower defense on the infinnity would turn blade fury into a very viable immune solution. You could even use an Ethereal one for highest damage, as Blade Fury doesn't wear off your weapon.